As a conventional image forming device that uses an electrographic process, such as a printer, a photocopy machine, a facsimile machine and an electrographic color recording device, a device that is, for example, disclosed in Japanese laid-open patent application publication number 2007-225969 is known. In the device, there is a belt in which a light reflection ratio of an entire belt is kept within a certain range by defining characteristics relating to surface roughness and a mirror specularity (MS), which is an indicator of condition or degree of a mirror surface, and so on of an entire belt surface that transfers a toner image on a recording medium or the like.
However, because light quantity of specular reflection light at a belt surface is largely different among several portions of the entire belt surface when interference fringes are generated on the belt surface in the device with the structures discussed above, there was a problem that toner image density that was transferred on the belt cannot accurately be detected.
The present invention is made in view of the problem mentioned above. An object of the present invention is to provide a belt device that includes a belt that is explained below, a transferring unit that includes the belt device and an image forming device that includes the transferring unit. The belt has the following characteristics. Toner image density that was transferred on the belt can be detected with a high degree of accuracy by preventing an occurrence of interference fringes on the belt and by keeping a light reflection ratio of the entire belt surface within a certain range.